The Bertha repair starts with seals.

In the first major piece to get replaced in the world’s largest tunnel-boring machine now sitting broken apart in downtown Seattle—part of the machine underground and the cutter head sitting on the surface—crews for Seattle Tunnel Partners and Hitachi installed the new outer seal ring.

Last week crews lowered the new outer seal ring into place, marking the first new piece installed in the machine as part of the contractor’s effort to resume tunneling.

The replacement outer seal system arrived in October and was stored on-site in downtown Seattle. The new inner seal system arrived the final week of May and installation started following the outer seal work.

The entire machine was originally constructed by Hitachi, a Japanese-based manufacturer, so Hitachi also built the replacement parts. The new seal systems include added reinforcement throughout to try to limit debris and contamination from entering the main bearing drive and cutter head. The new system’s design includes easier access to the seals, should the need again arise.

Washington State Dept. of Transportation, the project owners, have repeatedly stated that all repair efforts remain the responsibility of STP and Hitachi.

Here’s a look at some of the recent work on Bertha’s replacement via WSDOT photos:

Outer seal installation (above and below)

Reinforcing the outer shield (above and below)

Cleaning of a cutter drive motor

Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He also writes for Popular Mechanics, Sports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.